The development of high energy battery systems requires the compatability of an electrolyte possessing desirable electrochemical properties with highly reactive anode materials, such as lithium, sodium, and the like, and the efficient use of high energy density cathode materials, such as manganese dioxide. The use of aqueous electrolytes is precluded in these systems since the anode materials are sufficiently active to react with water chemically. It has, therefore, been necessary, in order to realize the high energy density obtainable through use of these highly reactive anodes and high energy density cathodes, to turn to the investigation of nonaqueous electrolyte systems and more particularly to nonaqueous organic electrolyte systems.
The term "nonaqueous organic electrolyte" in the prior art refers to an electrolyte which is composed of a solute, for example, a salt or complex salt of Group I-A, Group II-A or Group III-A elements of the Periodic Table, dissolved in an appropriate nonaqueous organic solvent. Conventional solvents include propylene carbonate, ethylene carbonate or .gamma.-butyrolactone. The term "Periodic Table" as used herein refers to the Periodic Table of the Elements as set forth on the inside back cover of the Handbook of Chemistry and Physics, 48th Edition, the Chemical Rubber Co., Cleveland, Ohio, 1967-1968.
A multitude of solutes is known and recommended for use but the selection of a suitable solvent has been particularly troublesome since many of those solvents which are used to prepare electroyltes sufficiently conductive to permit effective ion migration through the solution are reactive with the highly active anodes mentioned above. Most investigators in this area, in search of suitable solvents, have concentrated on aliphatic and aromatic nitrogen- and oxygen-containing compounds with some attention given to organic sulfur-, phosphorus- and arsenic-containing compounds. The results of this search have not been entirely satisfactory since many of the solvents investigated still could not be used effectively with high energy density cathode materials, such as manganese dioxide (MnO.sub.2), and were sufficiently corrosive to lithium anodes to prevent efficient performance over any length of time.
Although manganese dioxide has been mentioned as a possible cathode for cell applications, manganese dioxide inherently contains an unacceptable amount of water, both of the adsorbed and bound types, which is sufficient to cause anode (lithium) corrosion along with its associated hydrogen evolution. This type of corrosion that causes gas evolution is a serious problem in sealed cells, particularly in miniature type button cells. In order to maintain overall battery-powered electronic devices as compact as possible, the electronic devices are usually designed with cavities to accommodate the miniature cells as their power source. The cavities are usually made so that a cell can be snugly positioned therein thus making electronic contact with appropriate terminals within the device. A major potential problem in the use of cell-powered devices of this nature is that if the gas evolution causes the cell to bulge then the cell could become wedged within the cavity. This could result in damage to the device. Also, if electrolyte leaks from the cell it could cause damage to the device. Thus it is important that the physical dimensions of the cell's housing remain constant during discharge and that the cell with not leak any electrolyte into the device being powered.
U.S. Pat. No. 4,133,856 discloses a process for producing an MnO.sub.2 electrode (cathode) for nonaqueous cells whereby the MnO.sub.2 is initially heated within a range of 350.degree. C. to 430.degree. C. so as to substantially remove both the adsorbed and bound water and then, after being formed into an electrode with a conductive agent and binder, it is further heated in a range of 200.degree. C. to 350.degree. C. prior to its assembly into a cell. British Pat. No. 1,199,426 also discloses the heat treatment of MnO.sub.2 in air at 250.degree. C. to 450.degree. C. to substantially remove its water component.
U.S. application Ser. No. 051,491 filed on June 25, 1979 discloses a nonaqueous cell employing among other components a 3-methyl-2-oxazolidone-based electrolyte and a manganese dioxide-containing cathode wherein the water content is less than 1 weight percent based on the weight of the manganese dioxide.
Fluorinated carbon cathodes are disclosed in U.S. Pat. Nos. 3,536,532 and 3,700,502 as having the formula (CF.sub.x).sub.n wherein x varies from 0.5 to about 1.0. The cathodes are stated as being extremely stable and resistive to chemicals over the range of x from 0 to about 1. U.S. Pat. No. 4,139,474 discloses (C.sub.2 F).sub.n material.
It is an object of the present invention to provide a nonaqueous cell employing an MnO.sub.2 /(C.sub.y F.sub.x).sub.n cathode for nonaqueous cell systems.
It is another object of the present invention to provide an MnO.sub.2 /(C.sub.y F.sub.x).sub.n cathode for use with lithium anodes and various liquid organic electrolytes such as 3-methyl-2-oxazolidone in combination with at least one cosolvent and a solute.
It is another object of the present invention to provide a nonaqueous cell with an MnO.sub.2 cathode having a layer of (C.sub.y F.sub.x).sub.n.